This invention relates generally to wireless communication systems having adaptive antenna arrays and more particularly to full duplex adaptive antenna arrays in mobile communication systems.
Smart antennas, or adaptive antenna arrays, are proved to have distinct advantages in next generation wireless communication systems. The adaptive antenna array, usually deployed on a base station side of the wireless communication system, is capable of performing spatially selective communications (e.g., to transmit and receive) to optimize the signal-to-interference-and-noise-ratio (SINR) at a desirable receiving terminal, leading to significant increase of power efficiency and channel capacity on both the terminal-to-base-station (uplink) and base-station-to-terminal (downlink) communications in the wireless communication system. The basic concept of the adaptive antenna array system used in a wireless communication system can be dissected and summarized as the following four sequential steps:
(1) estimating the uplink wireless spatial signatures corresponding to all the active terminals based on the data received from the antenna array;
(2) performing the uplink beamforming for the active terminals based on the uplink spatial signatures;
(3) estimating the downlink channel characteristics or downlink spatial signatures; and
(4) performing downlink beamforming based on the downlink spatial signatures.
The spatial signatures are also known or referred to as channel characteristics which represent a changing model of the communication channel involved.
For a time-division-duplex (TDD) communication system which transmits and receives information in the same carrier frequency but different time slots, the downlink spatial signatures are identical to the uplink spatial signatures if the terminal is fixed according to the reciprocity principle. However, for moving terminals, especially fast moving terminals, the uplink spatial signatures and downlink spatial signatures may not be the same due to the physical displacement of the terminal made between the uplink time slot and downlink time slot. As a matter of fact, a 5 ms separation in time can cause quite a significant change of the spatial signatures if a terminal moves at a speed above 50 miles per hour.
Therefore, in the case of dealing with a moving terminal, channel prediction techniques must be applied to predict downlink spatial signatures based on the estimated uplink spatial signatures, knowing that they will be different to a certain extent. Existing channel prediction techniques are only applicable to a single antenna system and no effective channel prediction algorithm has been proposed or known to handle the channel prediction of an antenna array system. What is needed is a method for estimating the spatial signatures or characteristics of multiple channels in a telecommunication system.
This need for estimating the spatial signatures is also important in a frequency-division-duplex (FDD) communication system. In such a system, even if the terminal is fixed, the downlink spatial signatures are significantly different from the uplink spatial signatures due to the significantly different carrier frequencies used for both the uplink and the downlink, except for a few exceptional scenarios (e.g., only one direct path with no multipath). Also, it is deemed to be practically impossible to derive the downlink spatial signatures from the uplink spatial signatures. Therefore, to effectively implement a full duplex smart antenna system, it is ideal to feedback the downlink spatial signatures continuously from the terminal to the base station. Although it seems to be a good solution, it is hardly useful in a typical mobile communication system since this scheme requires too much overhead to feedback the downlink spatial signatures to the base station especially if the downlink spatial signatures change rapidly due to a fast moving terminal.
What is needed is a feasible method and system for realizing the full duplex adaptive antenna array for a telecommunication system.
In one example of the present invention, a method is disclosed for estimating a first wireless communication channel (FWCC) transmitting data from a first antenna system (FAS) to a second antenna system (SAS) in a telecommunication system. The telecommunication system has a second wireless communication channel (SWCC) for transmitting data from the SAS to FAS. First, one or more characteristics of the SWCC (SWCC Characteristics) are analyzed based on a data stream received by FAS from the SAS. An initial condition of the FWCC is also extracted from the data received. One or more characteristics of the FWCC (FWCC Characteristics) are then predicted based on the analyzed SWCC Characteristics and the extracted initial condition of the FWCC.
In another example of the present invention, a method is disclosed for estimating a first wireless communication channel (Downlink Channel) transmitting data from at least one antenna system to a communication terminal (CT) in a telecommunication system, the telecommunication system having a second wireless communication channel (Uplink Channel) for transmitting data from the CT to the antenna system. One or more characteristics of the Uplink Channel (Uplink Channel Characteristics) are analyzed based on a data stream received by the antenna system from the CT, and an initial condition of the Downlink Channel is also extracted from the data received. Based on the analyzed Uplink Channel Characteristics and the extracted initial condition of the Downlink Channel, one or more characteristics of the Downlink Channel (Downlink Channel Characteristics) are predicted.
In another example of the present invention, various channel estimation methods can be used for analyzing the Uplink Channel Characteristics and predicting the Downlink Channel Characteristics relying on the fact that the data stream has a plurality of data segments whose Doppler frequencies are close to each other to the extent that the Doppler frequencies are deemed as the same for the purpose of analyzing the Uplink Channel Characteristics.
In another example of the present invention, all the above-described techniques are applied to a telecommunication system whose antenna system is an antenna array.
In yet another example of the present invention, all the above-described techniques are applied to a telecommunication system using CDMA technologies or OFDM technologies.
The present invention can be applied to a telecommunication system communicating with a mobile terminal as well as a fixed terminal. The present invention also enables full duplex adaptive antenna array in mobile communication systems to significantly increase system capacity and coverage, and mitigate or eliminate the fast fading effect in dealing with fast moving mobiles.